Certain communications systems use optical couplers to route light signals throughout a network. The couplers combine signals from two or more optical fibers or split signals from, for example, a single fiber to two or more fibers. These couplers are typically formed by first stripping and cleaning two or more optical fibers in the regions of the fibers that are to be fused together, twisting these fibers about each other, and then heating the twisted region with a heat source while simultaneously pulling the fibers so that the fibers in that region fuse together. Finally, the fused region is epoxied into a substrate, such as, for example, fused silica, ceramic, or Invar to provide support. The entire fabrication process of the coupler has been performed manually.
Such optical couplers have been accepted in the industry, and they are considered to perform reasonably well for their intended purpose. However, they are not without their shortcomings. In particular, there are certain drawbacks of using a manual fabrication approach to produce couplers. For instance, there is a large variation in the quality of the final products associated with the wide tolerances which typify manual fabrication processes. Because there are many different grades of couplers produced with manual processes, the yield of high quality couplers tends to be low. It is desirable therefore to produce optical couplers with tighter tolerances and a higher yield.
The present invention greatly reduces problems encountered in the aforementioned manual fabrication processes. The present invention provides an automated system to produce optical couplers with minimal operator intervention.
In one aspect of the invention, an automated fusion system includes a draw assembly for holding optical fibers and for applying a tension to the fibers. The fibers are held substantially parallel to each other in the draw assembly. The system also includes a removal station that etches or strips buffer material from the fibers after the fibers have been placed in the draw assembly, and a heater or torch assembly for heating the fibers as the draw assembly applies a tension to the fibers in a manner that causes the fibers to couple or fuse together to form a coupler region. In addition, a packaging station is used to secure a substrate to the coupler region of the fibers to form the optical coupler.
Typically, the system includes a controller to control the functions of the draw assembly, removal station, torch assembly, and packaging station. The controller can also facilitate monitoring the functions of the draw assembly, removal station, torch assembly, and packaging station.
Embodiments of this aspect can include one or more of the following features. In some embodiments, the system includes an optical detector for monitoring the extent of the coupling while the optical coupler is being formed, and the removal station includes a removal heater assembly for heating acid used to strip the buffer material. The removal station can be provided with a thermocouple to measure the temperature of the acid, and the removal heater assembly can include a heater coil spirally wound around a mandril which contains an electrical heating cartridge.
In other embodiments the removal station is provided with an acid inlet and an acid drain hole, and a rinse water inlet hole and a water drainage hole. Typically, the removal station includes an acid etching section which facilitates formation of a meniscus of acid in which the fibers reside while being stripped of buffer material, as well as a rinse section which facilitates formation of a meniscus of rinse material in which the fibers reside while being rinsed of acid. In many embodiments, the removal station uses sulfuric acid to strip the buffer material, and de-ionized water to rinse the acid from the fibers. The sulfuric acid is usually heated to a temperature of about between 160xc2x0 C. to 200xc2x0 C.
In certain embodiments, the draw assembly includes a pair of vacuum chucks, which can be provided with a V-groove in which the fibers are positioned such that the vacuum chucks are coupled to a vacuum source which creates a suction along the V-grooves. Typically, the vacuum chucks are drawn apart at a rate of about between 50 microns/sec to 500 microns/sec.
In some embodiments, the torch assembly includes a ceramic torch which uses hydrogen fuel to produce a flame at the bottom of the ceramic torch. The torch assembly can include a fork plate provided with connector ferrules through which a vacuum is drawn that causes the fibers to be in contact. Generally, the fork plate and the ceramic torch are independently movable relative to each other. The fork plate can include a strip heater for evaporating residual water and acid from the fibers.
The packaging station can include a base provided with at least one slot into which the substrate is placed. The base is typically connected to a vacuum source which draws a vacuum through a hole in the slot to create a suction to hold the substrate in place. Epoxy can be placed at opposite ends of the substrate, and the system can include a UV curing light which emits radiation to cure epoxy after the fibers have been placed in the substrate.
In some embodiments, the system includes a fluid delivery system for delivery of acid and water to and from the removal station, and the delivery system includes a valve control box. The valve control box can include one or more solenoid valves to control the flow of acid, rinse water, and waste products.
The fluid delivery system can specifically include an acid delivery system, a water delivery system, and a vacuum fluid removal system. In some embodiments, the water delivery system includes a reservoir arranged such that the water is fed to the removal station by gravity, and the acid delivery system includes a supply line for transmitting acid to the removal station. Typically, the supply line has one end placed in an acid supply container, and an opposite end provided with a constrictor to maintain the supply rate of acid to the removal station. The acid delivery system can include a pump which in combination with the constrictor maintains the supply rate of acid to the removal station. The acid delivery system can also include a manometer to visually monitor the supply pressure of the acid to the removal station, and to provide a relief path in the event that the constrictor clogs up with debris. The acid delivery system can include a regulator which prevents backflow of acid from the manometer to the removal station in the event that the supply pressure is inadequate.
Related aspects of the invention include a method for forming an optical coupler. In this method, optical fibers are positioned on a draw assembly and a substrate is loaded in a packaging station. A portion of the fibers is placed in an acid bath of an removal station to strip buffer material from the fibers, and the fibers are rinsed after the acid bath to remove residual acid. Heat is applied to the rinsed region of the fibers to remove remnant liquid acid and water. A vacuum is drawn through a set of connector ferrules to hold the fibers together, and a tensile force is applied to the fibers with the draw assembly. While applying a tensile force to the fibers, a flame from a torch is applied to the fibers in a manner so that the combination of the tensile force and the heat from the flame causes the fibers to fuse together to form a coupler. Finally, a substrate is attached to the fibers to protect the fused region of the fibers to form the optical coupler.
Embodiments of this aspect can include securing the fibers to a set of chucks with a vacuum, filling a basin with acid to form a meniscus of acid in which the fibers reside, and subsequently draining the acid, and filling another basin with water to form a meniscus of water in which the fibers reside during the rinsing process, and subsequently draining the water. The fibers can be rinsed a second time.
In some embodiments, while the tensile force and heat are applied to the fibers, a laser light is activated to supply light at one end of one of the fibers to facilitate monitoring the coupling of the fibers. A coupling ratio or fixed length draw can be chosen, and the data related to the coupling process can be recorded. Also, the method can include placing the fibers in epoxy provided at each end of the substrate, and activating a UV light source to cure the epoxy once the fibers are placed in the substrate.
Among other advantages, the fusion process is entirely automated. The operator merely initializes the positions of the fixtures and stages, places unstripped fibers onto the drawing chucks and loads substrates with preloaded adhesive on the packaging station, and then activates the computer control program to initiate the fabrication process. The remaining steps are performed automatically under computer control. After the fusion process is complete, the operator removes the completed coupler from the station and places a new set of fibers on the drawing chucks for the next draw.
This automated process minimizes insertion losses because the fusion process is performed with tighter tolerances than manual processes. Because the stripping and the cleaning of the optical fibers is performed in the draw station immediately prior to the fusion process, there is an increased likelihood of preserving the cleanliness of the fibers during the draw. Further, the stripped fibers can be aligned and positioned at the same place relative to the alignment mechanism, thereby facilitating a more consistent fabrication process.
The use of connector ferrules for holding the fibers in place provides for a low cost precision vacuum assembly, because the ferrules can be readily made repeatedly with very tight manufacturing tolerances. Vertical motion of the torch assembly facilitates moving the torch only a small distance to remove the flame from the fibers which provides added versatility in the process control. Moreover, because the epoxy is applied to the supporting substrate prior to the mounting of the fiber in the fusion assembly, there is no time-consuming application of the adhesive while the coupler is located in the fusion system.